Choroideremia

Sex linked inheritance

Choroideremia is a rare, inherited disorder that leads to progressive loss of vision due to degeneration of the choroid, retina, and retinal pigment epithelium. This condition primarily affects males, as it is passed down through an X-linked recessive pattern. The gene responsible for choroideremia is the CHM gene, which encodes the Rab escort protein-1 (REP-1). Mutations in the CHM gene lead to a deficiency of REP-1, disrupting intracellular traffic and leading to the degeneration of retinal cells.

Symptoms

The initial symptoms of choroideremia often appear in childhood, starting with night blindness and a narrowing field of vision. As the condition progresses, individuals experience a further reduction in their peripheral vision, eventually leading to tunnel vision. In the final stages, this can result in complete blindness. Some individuals may also experience a decrease in central vision acuity as the disease advances.

Diagnosis

Diagnosis of choroideremia is primarily based on the clinical history and examination findings, including a detailed family history due to its hereditary nature. Diagnostic tests such as fundus photography, electroretinography (ERG), and optical coherence tomography (OCT) are used to assess the extent of retinal degeneration and confirm the diagnosis. Genetic testing can identify mutations in the CHM gene, providing a definitive diagnosis and aiding in family planning and genetic counseling.

Treatment

As of now, there is no cure for choroideremia. Treatment focuses on managing symptoms and maximizing the remaining vision. This includes the use of low-vision aids and adaptive technologies to help individuals maintain independence. Regular monitoring by an ophthalmologist is essential to manage any complications that may arise, such as cataracts or retinal detachment.

Recent advances in gene therapy have shown promise in treating choroideremia. Clinical trials involving the replacement of the defective CHM gene with a healthy version have demonstrated potential in slowing or even halting the progression of the disease. However, these treatments are still under investigation and are not yet widely available.

Prognosis

The prognosis for individuals with choroideremia varies. The progression of vision loss is gradual but inevitable, typically leading to significant visual impairment or blindness by middle age. However, the rate of progression can vary widely among affected individuals. Early diagnosis and intervention with low-vision aids and supportive services can help individuals adapt to their changing vision and maintain a high quality of life.

Epidemiology

Choroideremia is considered a rare disease, affecting approximately 1 in 50,000 to 100,000 individuals worldwide. It primarily affects males due to its X-linked inheritance pattern, although female carriers may exhibit mild symptoms due to lyonization (X-chromosome inactivation).

See Also

• Retinal diseases
• Genetic disorders
• Gene therapy